Trees produce pollen. Lots of it. Even if you aren't normally allergic, the air is so full of pollen it can look like it's snowing ... and that much particulate stuff in the air is going to cause irritations to the breathing apparatus of anything that breathes.
Pollen is one kind of particulate, but there are plenty more. It adds up to a level of dust and dirt that's hard to imagine. You can't clean fast enough to keep up with it, even if you clean all the time. Eventually you give in and adopt the attitude that dust is a protective layer provided my nature.
Between the dog hair, the pollen and the dust ... your standards have to come down to earth. Reality bites, but comes the Autumn, for a month and some, it's so beautiful for once, you lose your breath to the beauty, not the stuff floating in the air.